Research On State Estimation Of Distribution System Integrated With Distributed Generations

With the rapid development of active distribution network and distributed generation(DG)technology,more and more DGs have been connected to distribution network on a large scale.The access of large number of DGs will change the basic pattern of unidirectional power flows in traditional distribution network,and may seriously affect voltage distribution,network structure,power consumption,and power supply reliability.These bring severe challenges to modern distribution management system.As a basic function of the advanced application software of the distribution management system,state estimation distribution of system needs to obtain the real-time operating status of the entire system more quickly and accurately,to provide reliable data for reasonable allocation of DG output and load power,optimization of active and reactive power in distribution network and self-healing technology.Through the supervisory control and data acquisition(SCADA),the traditional state estimation of distribution system acquires various measurement data,including power measurement of substation nodes,voltage amplitude measurement of some nodes and current amplitude measurement of some branches.These data have few data type,poor accuracy and slow update speed,so it is difficult to meet the requirements for the state estimation of distribution system with DGs.With the rapid development of global positioning system(GPS),wide area measurement system(WAMS)based on phasor measurement units(PMU)is gradually applied to distribution network.Compared with traditional SCADA,WAMS has the advantages of high measurement accuracy,wide cover range,and high transmission speed.However,due to economic and technical limitations,these two types of measurements will coexist for a long time in the future.How to make full use of the WAMS measurement information in the state estimation of distribution system with DGs is of great significance.In addition,in the state estimation of distribution system,DG output and load power are usually in the form of pseudo-measurement.In the face of the uncertainties brought by DG and load pseudo-measurement,how to consider the impact of various uncertain factors on the state estimation of distribution network is also an urgent problem to be solved.Therefore,based on the research on state estimation of distribution system at home and abroad,this paper mainly studies the state estimation of distribution system with DGs from the following aspects:Firstly,according to the operating characteristics of different DGs.the DG model without measurement in state estimation is established based on the active power prediction of DG.Secondly,the state estimation model of distribution system with DGs,considering hybrid measurement,is established-The model effectively compensates the insufficiency of low estimation accuracy of the traditional branch current method when the voltage amplitude of the root node is not correct.And this model focuses on the data-matching problem of mixed measurement,and it does not require the conversion of GPS reference point or artificially defined reference point,avoiding the influence of phase angle estimation error at the reference point.By eliminating related branches,this model reduces the state variable dimension and makes sure that the zero injection nodes injection current estimation is strictly zero.Finally,based on affine mathematics,the influence of the uncertainty of different DGs and load pseudo-measurements on state estimation of distribution system is further studied.The above study is evaluated through the case simulation.